1. Field of the Invention
The invention relates to a water soluble polymer dispersion comprised of at least one water soluble monomer, at least one hydrophobic monomer, and optionally at least one amphipathic monomer, as monomer components.
2. Discussion of the Background
Aqueous dispersions of water soluble polymers are employed, e.g. as flocculants in waste water treatment, as dewatering agents when removing an aqueous phase, as retention agents in paper manufacturing, as soil conditioners, or as dispersants.
EP 170,394 describes a water-miscible liquid comprised of particles which are comprised of a high molecular weight polymer gel, with particle sizes &gt;20 .mu.m, in aqueous solution. The continuous phase is an aqueous solution containing an equilibrating agent which maintains the water content of the gel particles in equilibrium with the water content in the continuous phase, thereby preventing agglomeration of the gel particles. Preferred equilibrating agents are the sodium salt of polyacrylic acid, or polydiallyl dimethylammonium chloride (poly--DADMAC).
In EP 183,466, a method of manufacturing a water soluble polymer dispersion is described, characterized by polymerization of a water soluble monomer under stirring in an aqueous solution of at least one salt in the presence of a dispersing agent. Employed are polyols, polyalkylene ethers, alkali salts of polyacrylic acid, and alkali salts of poly-2-acrylamido-2-methylpropanesulfonic acid, as dispersants or as salts which do not solvate the polymer in aqueous solution.
DE 2,924,663 concerns a method of manufacturing an aqueous dispersion from a water soluble polymer composition with good stability and flowability, wherein the water soluble polymer contains at least one water soluble ethylenically unsaturated monomer, and certain substances which may be present as dispersants, e.g. polyalkylene ethers, polyethyleneimine, etc., possibly in the presence of inorganic salts. The aqueous dispersion thus produced may be used as a flocculant, thickener, soil conditioner, or for other applications, possibly after dilution with water.
In JP 59-108,074, thickeners are described which are comprised of polymers in aqueous solution, having monomer units of (meth)acrylic acid and/or salts of same, and (meth)acrylamide, and methyl- or ethyl acrylate; polyethylene glycol is employed as a dispersant.
A drawback of the gel-particle-containing aqueous solutions described in EP 170,394 is that their viscosities increase sharply upon long standing; and shear gradients (e.g. by stirring) are needed to reduce the viscosity. The properties of the liquid depends on a complex equilibrium between the polymer, the equilibrating agent, the water content, and the particle size of the gel particles.
EP 183,466 reports water soluble polymers as dispersions in aqueous salt solutions, achieved with the aid of a dispersant. A drawback of such dispersions is the high salt content of the aqueous phase (up to 30 wt. %) as compared with a relatively low polymer content (the polymer being the effective component) (up to 20 wt. %); in certain applications of such dispersions this results in waste water problems.
Aqueous dispersions according to DE 2,924,663 have the drawback of high proportions of dispersant compared to the amount of water soluble polymer. If such dispersions are employed, e.g., as flocculants for electrically charged particles, the effectiveness of the high molecular weight ionic polymer is reduced by the presence of the dispersant, which has a relatively low molecular weight compared to that of said ionic polymer.
The polymers with thickening action produced according to JP 59-108,075 have mean molecular weights (M.sub.w, gravimetric mean) between c. 100,000 and 500,000 Dalton, which is clearly too low for use as flocculants.
Accordingly, the state of the art presented above leads to the problem of devising aqueous dispersions of water soluble polymers which have low viscosity, a high content of the polymeric active component, high molecular weight of said polymer, and a salt-free aqueous phase.